The term "optical system" as used herein refers to any system that utilizes light waves to convey information between one node and one or more other nodes.
Telecommunications carriers began installing optical fiber cable about 15 years ago. At the time the optical fiber cables were installed, it was expected that the optical fiber infrastructure would provide communications systems and networks with ample capacity for the foreseeable future. However, the phenomenal growth of data traffic on the Internet has taxed the capabilities of the optical fiber infrastructure. In addition, new high bandwidth applications are being developed and are being made available for corporate applications. The result of this increased usage of the fiber infrastructure is serious network congestion and exhaustion of the fiber infrastructure. In the past, optical fiber systems relied on time division multiplexing to route traffic through a channel. Time division multiplexed systems add more capacity by time multiplexing signals onto an optical fiber. A disadvantage of time division multiplex systems is that data must be converted from light waves to electronic signals and then back to light. The system complexity is thereby increased.
Wavelength Digital Multiplexing (WDM) and Dense Wavelength Digital Multiplexing (DWDM) are being used and/or proposed for use in long-haul telecom network applications for increasing the capacity of existing fiber optic networks. The advantage of both WDM and DWDM is that conversion to electrical signals is not necessary. The devices that handle and switch system traffic process light and not electrical signals. In WDM, plural optical channels are carried over a single fiber optic, with each channel being assigned to a particular wavelength. Each transmitter includes a laser that is intended to operate at only one of the allowed wavelength channel frequencies. Each laser is engineered to operate within the channel specifications for the life of the system. For repair purposes, an inventory of transmitters for each wavelength channel must be maintained. As the number of channels increases, the size of the inventory likewise increases. DWDM is a WDM system in which channel spacing is on the order of one nanometer or less. WDM and DWDM expand the capacity of an optical fiber by multiple wavelength channels into a single laser beam. Each wavelength is capable of carrying as much traffic as the original. The need for maintaining a large inventory of transmitters is likewise an issue for DWDM systems.
It is highly desirable to provide an integrated optic device for selection of a desired wavelength for use in a tunable optical transmitter as well as in a tunable light source.